Energy

Lanzhou University Scientists ‘Bottle’ Sunlight to Produce Hydrogen On Demand in the Dark

Ritambhara K

December 29, 2025
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Researchers at China’s Lanzhou University have created a system that stores solar energy in a liquid solution for hours and uses it to produce hydrogen fuel in total darkness. Using inexpensive, commercial materials, the team achieved a record-setting dark hydrogen evolution rate, pointing toward a future where solar energy could be transported as a stable chemical liquid and converted to fuel anywhere, anytime.

Imagine capturing the abundant sunlight of a desert, storing its energy in a simple liquid, and shipping it to a cloudy city where hydrogen gas is produced on demand—no power grid, no high-pressure tanks, just a catalyst added to a solution. This vision of decoupling solar energy harvesting from its use has taken a significant step toward reality thanks to a clever chemical workaround.

The persistent challenge with solar hydrogen production is its reliance on constant light. Night and clouds stop the process dead. Furthermore, storing and transporting the resulting hydrogen gas is notoriously difficult and expensive, requiring extreme compression or cryogenic temperatures. Nature, however, provides a blueprint. Plants store solar energy in chemical intermediates during the day and use that stored energy to build sugars later, in the dark.

Scientists have long sought an artificial equivalent. A breakthrough, published in the journal Advanced Materials, now demonstrates this “dark photocatalysis” using only two off-the-shelf materials, with no need for external power. The team, led by researchers from Lanzhou University, combined graphitic carbon nitride (g-C₃N₄), a light-absorbing semiconductor, with ammonium metatungstate (W₁₂), a type of polyoxometalate that acts as a molecular battery.

Here’s how it works: In a solution with a sacrificial reagent (like methanol), sunlight hits the carbon nitride, generating electrons. These electrons are rapidly shuttled to and stored within the neighboring W₁₂ clusters, a process visible as the solution turns from pale yellow to deep blue. The energy is effectively “bottled.” Later, in complete darkness, introducing a common platinum catalyst triggers the release. The stored electrons combine with protons in the solution to form hydrogen gas bubbles.

The system’s elegance lies in its simplicity and the favorable chemistry between the two components. Under acidic conditions, they form a tight electrostatic bond, ensuring efficient electron transfer. “The conduction band of g-C₃N₄ and the reduction potential of W₁₂ are well matched,” the researchers noted, enabling spontaneous energy storage. Among several materials tested, this pairing proved most effective.

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The performance metrics are compelling. After one hour of illumination, the system produced 13.5 µmol of hydrogen in the following dark phase. It achieved a maximum dark hydrogen evolution rate of 3220 µmol g⁻¹ h⁻¹, which, according to the paper, is a record for all reported dark photocatalytic systems. Crucially, outdoor tests under natural sunlight confirmed real-world viability, producing hydrogen at a rate of 954 µmol g⁻¹ h⁻¹ after the sun went down.

This research, reported by Nanowerk, demonstrates a critical proof of concept: the decoupling of light capture and fuel production. The system maintained its functionality over multiple charge-discharge cycles, showing promising durability. While significant hurdles remain—particularly proving the solution can retain its charge for days or weeks necessary for transport—the fundamental barrier has been crossed.

“The research demonstrates that simple electrostatic assembly of commercial components can store solar energy and convert it to hydrogen in complete darkness without external power,” the study concludes. If the stability of the charged liquid can be extended, it could revolutionize energy logistics, enabling sunny regions to export their solar wealth as a safe, stable liquid to power industries and cities across the globe.